1857.] of Gold (and other Metals) to Light. 417 



minated by the sun's rays and a lens, appeared to give a 

 fine green reflexion, but whether this is a true colour as com- 

 pared to white light, or only the effect of contrast with the 

 bright ruby in the other parts of the fluid, I am not prepared 

 to say. 



When the deposits were examined in the dark tube by trans- 

 mitted light, being first diffused in more or less water to give 

 them the form of fluid, those first deposited, and therefore pre- 

 sumed to be the heavier and larger, transmitted a pure blue 

 light. The second and the third had the same character, 

 perhaps the fourth, if the subdivision into portions had been 

 numerous ; then came some which transmitted an amethystine 

 ray from the white of paper ; and others followed progressing 

 to the finest, which transmitted a rich ruby tint. It is probable 

 that many of these deposits were mixtures of particles having 

 different characters, and this is perhaps the reason that in some 

 cases, when the fluids were contained in round-bottomed flasks, 

 the lens-like deposit was ruby at the edges, though deep violet 

 in the middle, the former having settled last ; but as a pure 

 blue deposit could be obtained, and also one transmitting a 

 pure ruby ray, and as a comparatively pure intermediate pre- 

 paration transmitting a ruby violet, or amethystine ray, was 

 obtained, it is probable that all gradations from blue to ruby 

 exist; for the production of which I can see no reason to 

 imagine any other variation than the existence of particles of 

 intermediate sizes or proportions. 



When light other than white was passed through the fluids, 

 then of course other tints were produced, yet some of these 

 were unexpected. A fluid of a pure blue colour, whilst in the 

 dark tube, would in an open glass and by reflected light appear 

 of a strong ruby-violet tint. Dropping some of the wet deposit 

 into pure water, the striae which it formed would in one part 

 be ruby in colour and in another violet: these effects were 

 referable to the light reflected from the solid particles back 

 through the fluid to the eye, but it seemed redder than any 

 which light reflected from gold was likely to produce. How- 

 ever, upon regarding the surface of dull gold-leaf, or the thick 

 wet deposit of gold, or the hand, it was found that the red rays 

 easily passed through the blue fluid and formed a ruby-violet 

 tint. Prevost showed in old times, how much the red and 



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